Method of and means for exhausting to low pressures



0. E. BUCKLEY.

METHOD OF AND MEANS FOR EXHAU STING TO LOW PRESSURES.

APPLICATION n20 MAY 8, 1916.

Patented (m 24, 1922.,

l H v e 177'0 M- roan.

METHUB UFAND MEANS JFQR EXHAUSTING Lltl G? application. tiled may a,

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concise, and exact description.

This invention relates to the exhausting oi vessels to low pressures, and particularly to a new and improved method and means for this purpose.

lit has, of course, been well lrnownthat the exhaustion of vessels to low pressures is facilitated by boiling mercury inside of them during the exhausting process. it has been found that in this way, by the use of a comparatively rough pump, pressures can be obtained considerably below those to which said pump will exhaust when mercury vapor is not present within the vessel; and it is supp osed that this lmprovement 1n results is due to the fact that the mercury molecules, when leaving the vessel which is being exhausted, carry along with them molecules of the air which it is desired to remove.

Attempts, however, to adapt this principle to the exhaustion of vessels which do not contain mercury have disclosed that it is difficult to introduce into the mercury vapor stream the air molecules coming from the vessel to be exhausted. For example, it has been found that when the vessel to be exhausted is connected by a conduit with the conduit carrying the mercury vapor stream, the mercury molecules, instead of carryinp along the molecules of air from the vesse heat back the air molecules and prevent them from leaving the vessel. Attempts have been made to prevent this by introducing the mercury stream into the air stream from the vessel to be exhausted, in a direction substantially parallel to the direc tion in which the air stream is flowing. Such an arrangement, however, does not give entirely satisfactory results, owing probably to the fact that the mercury molecules which are moving in all directions, reboun from the walls of the conduit in all directions and beat baclt the air molecules, although this etlect is somewhat lessened it the rare. Serial We.

walls of the mixing chamber are cooled by a water jacket.

The present invention is the result of the discovery that it substantially all of the mercury molecules in the vapor stream are moving in directions substantially parallel withthe direction. of stream flow at the point where the air molecules from the vessel to be exhausted are introduced, the air molecules are not beaten back by the mercury molecules, but mingle with and are carried along by them. Ur stating it another wa r, iiin advance of the point where the air and vapor streams combine, most of the mercury molecules, which are moving transversely to the direction of stream flow, are removed from the stream, then the air molecules are not beaten back, but are carried along by the mercury molecules which are moving in substantially the same direction as the stream flow. The present method may therefore be described as consisting in drawing the gas from the into a vapor stream in which substantially all of the molecules are moving in directions substantially parallel to the direction of stream flow.

This improved. method of exhausting ves sels to low pressures will be fully understood from the following description oil a preferred from of apparatus for carrying it out. This apparatus is shown, to a oertain extent diagrammatically, in the accom panying drawing.

ln-the drawing, the vessel to be exhausted is indicated at 9,. A. plurality of such vessels may be connected to a conduit 3 leading through a liquid air trap A or wellknown form to a conduit l connecting with the vapor pump B, hereinafter described in detail. Connected to the vapor pum B is a pump 5, of any suitable type, which need not be capable of exhausting to the ex tremely low pressures which it is desired to obtain in the vessel 2, The liquid air trap A, as usual, comprises a doublewalled vessel 7, having the space between the walls exhausted to a fairly low pressure, which vessel contains liquid air, indicated at 8, into which dips the closed end 9 of the tube l, into which the end 10 of the tube 3 projects, as shown.

The vapor pump B, by which the vessel to be exhausted of exhaustion, forming the subject-matter of this invention, is carried out, comprises a tubeor conduit 12 terminatin at its lower end in an enlarged portion or bulb 13 containing a suitable liquid 14, such as mercury. The bulb 13 and the mercury 14 may 3 and the vessel to be exhausted, is connected to the conduit 12 as shown. Provision is made for cooling the conduit 12 from a point considerably below to a point considerably above the place where it is joined to the conduit 4, and also for cooling the lower end of the conduit 4. As shown, this means comprises a water jacket 20 enclosing the portions of conduits 12 and 4 just mentioned. A fiow of cold water" is maintained through this water 'acket 20 through the pipes 21 and 22, as indicated bythe arrows.

The apparatus above described operates in the following manner: By the heating of the mercury 14, a mercury vapor stream is o'ausedito pass upward through the tube 12. When this vapor stream first leaves the bulb 13, the mercury molecules are moving in all directions; but when the stream passes upward into that portion of. the conduit 12 which is cooled by the cold water in the water jacket 20, those mercury va or mole-. cules which impinge the cold wa is of the conduit are condensedand are removed from thevapor stream, eventually flowin down the walls of the tube 12 back into t e bulb 13. The result is that the mercury vapor molecules which proceed upward through the conduit 12, are for the mostpart moving substantially in the direction of stream flow. When this vapor'streampasses the point in the conduit 12 to which the conduit 4- is connected, most of the mercury vapor molecules go on, and not only do. not heat back the air molecules seeking to enter from the conduit 4, but actually en age with and carry along said. air mo ecules upward through the upper. partof the conduit 12. As this mixture of air and inercur molecules passes upward through the coo ed portion of the conduit 12, most of the mercury vapor molecules are 'condensed on the walls of said conduit and but little mercur vapor is mixed with the air which nally reaches the forepump 5. The water jacket 20 also serves to condense on the walls of the lower end of the conduit 4 some of the mercury vapor which may have passed. into that portion of the apparatus. The liquid air trap A condenses any other mercury vapor which may work back through the tube t to that point, and also serves in the usual manner to condense any vapors coming from the vessels to be exhausted.

From the foregoing description of the manner in which the apparatus shown operates, it will be apparent that it is highly advantageous to have the conduit carrying the mercury vapor stream cooled in advance of the point at which the air is introduced by the communicatingconduit which. extends to the vessel to be exhausted. This feature is an essential part of the present invention.

What is claimed is:

1. The method of exhausting as containing vessels which consists in rawing the gas from the vessel to be exhausted by a stream of vapor from which molecules moving in directions other than substantially parallel to the path of the stream have been removed whereby substantially all of the molecules in the stream are moving in approximately parallel directions.

2. The method of exhausting gas containing vessels to low pressures, which consists in roducin a stream of va or substantially reducing the number of molecules in said stream which are moving in paths not substantially parallel to the direction of stream flow, and then drawing gas from the vessel to be exhausted into said vapor stream.

3. In apparatus for exhausting gas containing vessels to loW pressures, means, including a conduit, arranged to provide a stream of vapor, means for leading to said stream gas from the vessel to be exhausted, and means for removing from said vapor stream, in advance of the place at which the gas from the vessel to be exhausted is led thereto, substantially all molecules whose paths are not substantially parallel to the direction of stream flow,

4, In apparatus for exhausting gas-containingvessels to low pressures, a source of vapor, a conduit through which said vapor passes, a branch conduit communicating with said first named conduit and adapted for connection with the vessel to be exhausted, and means for cooling the first named conduit at a portion in advance of the place at which said branch conduit connects with said first named conduit.

5. In apparatus for exhausting s-containing vessels to low pressures, a s urce of vapor, a conduit through which said vaporv passes, a branch conduit communicating with said first-named conduit and adapted for connection with the vessel to be exhausted, and means for cooling said first-named conduit at portions in advance of and beyond the place at which said branch conduit connects with said first-named conduit.

iaaaaaa it 6. Jim apparatus for exhausting gas con taming-vessels to low pressures, a source of vapor, a conduit through which said vapor passes, a branch conduit communicating with said first named conduit and adapted for connection with the vessel to be exhausted, and means for cooling the first named conduit and the branch conduit from points in advance of the place of union to a point beyond the place of union.

7. In apparatus for exhausting gas con taining vessels to low pressures, a conduit terminatin in a'bulb containin means for Eeating said bulb and't e mercury therein, a branch conduit communicating with said first named conduit andadapted for connection with the vessel to be exhausted, and means for cooling the first named conduit and the branch conduit from points in advance of the place of union to a point beyond the place 0 union.

mercury,

8. Apparatus for exhausting gas-containing vessels to' low pressures comprising in combination, a gas pump, conduit means arranged to provide a path of gas flow from the vessel to be exhausted to said pump, means for increasing the flow of gas along said path comprisinga-mercury reservoir, means for vaporizing the mercury in said reservoir, means for limiting the translational molecular movements in said vapor to substantially parallel paths to form a nondifiuse vapor stream and for directing said stream along a portion of the path of gas flow, and means for condensing said mercury vapor between its point of introduction into the path of gas flow and said pump, said means being arranged to permit the return of the condensed mercury to the reservoir.

In witness whereof, I hereunto subscribe my name this 5th da of -Ma A. ll, 1916.

OLIVl ER E. UC'KLEEY. 

